This invention relates to apparatus for adjusting a starting position of high speed injection in a die cast machine, and more particularly apparatus for maintaining the high speed injection starting position at a definite position.
It is necessary to accurately set a starting position of high speed injection of an injection machine for the purpose of obtaining high quality die cast products. As shown in FIG. 1, in a prior art die cast machine, a limit switch 12 is provided for the piston rod 10 of a die cast or injection machine to be actuated at a predetermined stroke of piston rod 10 so as to start a high speed injection at the predetermined stroke. The limit switch 12 is operated by a lever 14 interlocked with the piston rod 10, and a limit switch 16 actuated by the lever 14 is provided for limiting the return stroke of the piston rod 10.
According to another prior art apparatus a position detector of the piston rod is provided for detecting the stroke thereof, and when the stroke detected by the position detector and a predetermined stroke coincide with each other, an instruction signal is outputted to start high speed injection.
With this prior art apparatus, although the stroke position at which the start instruction for the high speed instruction can be maintained substantially constant, there is a certain time lag between the issuance of the starting instruction and the commencement of the high speed operation of the injection machine effected by a pressurized oil system. Consequently, as shown in FIG. 2, where the injection speed in a low speed injection region is fast (curve A) and low (curve B), although the stroke position S.sub.1 at which a starting instruction is issued is the same, the actual starting positions S.sub.A and S.sub.B of the high speed injection are not the same.